The present invention relates to a method and an apparatus for producing unidirectional materials to be used for flexbeams and spars for rotor blades of helicopters. More particularly, the present invention relates to a method and an apparatus for fabricating unidirectional materials particularly for helicopter parts, which enable an improvement in the strength of the fabricated unidirectional material in all directions thereof.
Heretofore, unidirectional materials to be used for flexbeams for helicopter blades have been fabricated by a method described, for example, in Japanese Patent Laid-Open Publn. No. 1-17810 (1990). According to the known method, a composite-material roving is delivered from a feeding mechanism of a filament winding device and is wound in a ring pattern between two or more parallel pins fixedly installed at spaced-apart positions.
A unidirectional material produced by the known method has a very high tensile strength in a longitudinal direction of the wound roving. However, with respect to tensile stress in a crosswise direction, perpendicular to the longitudinal direction, the strength of the fibers is not effective. For this reason, the strength of the resin bonding the roving determines the strength of the unidirectional material in the 90-degree direction. Consequently, the strength in the 90-degree direction is extremely low. That is, the tensile strength in the 90-degree direction is of the order of 5 percent or less of the strength in the 0-degree direction.
Accordingly, it has been practical in the past to reduce the tensile stress in the crosswise direction of the unidirectional material generated by torsion in the flexbeams accompanying feathering action of the rotor.
More specifically, attempts have been made to increase the strength through such measures as relieving stress concentration due to the shape of the flexbeams and adding doublers for reinforcing weak parts.
In all of these measures, however, the aim is only to reduce internal stress by load in the resin material. Consequently, there is a limit to the effectiveness of these measures. Moreover, there arises the problems of complication of the shape of the unidirectional material and increase in the number of parts.